1. Field of the Invention
This invention relates generally to devices which generate ozone by applying a high voltage alternating current across a gap to create a corona discharge, and more specifically to an ozone generator cell of the elongate concentric tube type which has an annular corona gap bounded by two surfaces at least one of which is a dielectric, and which is functional as an individual self-contained cell.
2. Description of the Prior Art
Ozone is a very powerful gaseous reactant, and its use has been well established for many years in a wide range of industrial applications. Recently its value in all types of water purification applications has been coming to the fore because of its ability to act as a powerful oxidant, microflocculant and disinfectant without producing toxic by-products.
The most widely used method of generating ozone is to flow dry air or oxygen through a narrow gap or annulus bordered on one side by a cooled stainless steel ground electrode and on the other by a dielectric electrode surfaced (on the side which faces away from the gap) with an electrical conductor. An alternating current of high voltage is connected to the dielectric electrode, producing a high voltage field across the gap which results in a corona discharge. This discharge, which is also known as a "silent discharge" or "cold plasma discharge" and is actually composed of many transient microdischarges, converts a percentage of the gas to ozone. The dielectric is necessary to prevent the microdischarges from becoming arcs, which would rapidly destroy the electrode surfaces.
The majority of high quality prior art corona ozone generators have been designed for very large-scale industrial-type applications, with dozens of glass tubes in a large boiler-like stainless vessel. Today there is a great need in numerous water treatment applications for high quality small and medium-sized individual (stand-alone) cells which are reasonable in cost and which can be maintained by people who do not have extensive training. Much of the prior art that has addressed this need has simply scaled down previous large-scale designs, and because they still retain many of the original design features require precision welding of stainless steel, are extremely expensive and are difficult to assemble and service. The less expensive prior art designs often do not maintain an accurate corona gap, the result being a decreased ozone production. In addition, most prior art designs for small individual cells have elastomeric seals which put pressure on either the inner wall or the butt ends of the dielectric tube, which are a tube's weak points, and this occasionally leads to breakage. Furthermore, the elastomeric material used for the seals in most prior art is slowly degraded by ozone. Also, prior art designs generally use only one seal between a cooling liquid and the corona cavity, which sometimes results in a gradual contamination of the corona cavity by coolant when temperature or pressure changes cause the seal to roll or "pump" slightly back and forth.